Thursday, March 13, 2014Last Update: 4:09 PM PT

FBI Agent Describes His Long Talk With Bin Laden's Son-in-Law

MANHATTAN (CN) - Osama bin Laden hand-picked his son-in-law to spread propaganda for the terrorist organization despite his initial objections, an FBI agent testified Thursday in the trial of the highest-ranking al-Qaida member yet to take place on American soil. FBI Agent Michael Butsch testified at the federal trial that Sulaiman Abu Ghaith promised to be honest with him during a 14-hour transatlantic flight to White Plains after Abu Ghaith was arrested last year. "He said he was close to Osama bin Laden but was not a member of al-Qaida," said Butsch, who was the first person to interview Abu Ghaith after his arrest. "He said he told bin Laden that he was new to the field and someone else was better suited. But Osama bin Laden wanted him to speak" for the terrorist organization. It was the sixth day of testimony in Abu Ghaith's trial, in a courtroom perched atop a high-rise courthouse just blocks from the World Trade Center. Butsch said that Abu Ghaith told him he had refused to fully pledge his allegiance to bin Laden - offering him only a "mini-bayat," or alliance - saying he was a scholar and orator, not a soldier. Yet even though the two men had "different beliefs" about jihad, he agreed to serve as al-Qaida's spokesman. In that capacity, he preached to recruits at al-Qaida training camps. The day after the Sept. 11, 2001 terrorist attacks, Butsch said, bin Laden gave Abu Ghaith "bullet points," as a guide for him to write a speech praising the attacks and threatening Americans. The tapes were then distributed as al-Qaida propaganda. One shows Abu Ghaith sitting next to bin Laden; another shows Abu Ghaith saying "the storm of airplanes will not abate." A third shows him warning American and British Muslims "not to board any aircraft and not to live in high rises." Butsch said that he "treated him [Abu Ghaith] like a gentleman, and he did the same to me" during the 12-hour flight to America. He said that Abu Ghaith was allowed to pray while on the plane and that they took multiple breaks during questioning. Busch said that there was even some "joking around," after he commented on Abu Ghaith's large biceps. "I said, 'You have some pipes there,'" Butsch recalled. "He smiled and said, 'I got them from doing push-ups. Thank you for noticing.'" Evan Kohlmann, a terrorism expert who has monitored terrorist propaganda dating back to 1998, also testified Thursday, telling the jury that before the popularity of the Internet, al-Qaida relied first on videos and audio recordings designed to "strike fear" in its enemies and recruit people who were "sympathetic" to its cause. He said the tapes were played at training camps as a way "to allow them to have a personal audience with would-be suicide bombers, to groom them for suicide missions." Abu Ghaith is charged with conspiring to kill U.S. citizens and aiding a terrorist organization. He could be sentenced to life in prison if convicted. Testimony continues Friday.